Firebug is an excellent option when working with Firefox, and Visual Studio is perfect for Internet Explorer. Until recently there was no good option for Google Chrome, but earlier this year Chrome updated the developer tools, and they rock.
Assuming you’re on a Windows machine, hit Control+Shift+J to open the developer tools window. You can also get there from the page menu, or by right clicking on any element in the page to “inspect element.”
The toolbar at the top lets you inspect the DOM elements, debug scripts, even inspect the cookies currently saved in the browser. It isn’t obvious from teh UI, but there are keyboard shortcuts for each of the debugger commands:
F8 - Run
F10 - Step over
F11 - Step into
Note that if the browser window is focused and not the debugger window, F11 will have the window go into full screen mode.
While I’ve found that Chrome is a phenomenal browser and I’m in love with its performance, it can be somewhat less forgiving of errors than other browsers. The Chrome debugger is an excellent tool for tracking down those errors.